In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: π) is any of three subatomic particles: π0, π+, and π−. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions π+ and π− decaying after a mean lifetime of 26.033 nanoseconds (2.6033×10−8 seconds), and the neutral pion π0 decaying after a much shorter lifetime of 85 attoseconds (8.5×10−17 seconds). Charged pions most often decay into muons and muon neutrinos, while neutral pions generally decay into gamma rays.
The exchange of virtual pions, along with vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but commonly are in high-energy collisions between hadrons. Pions also result from some matter–antimatter annihilation events. All types of pions are also produced in natural processes when high-energy cosmic-ray protons and other hadronic cosmic-ray components interact with matter in Earth's atmosphere. In 2013, the detection of characteristic gamma rays originating from the decay of neutral pions in two supernova remnants has shown that pions are produced copiously after supernovas, most probably in conjunction with production of high-energy protons that are detected on Earth as cosmic rays.The pion also plays a crucial role in cosmology, by imposing an upper limit on the energies of cosmic rays surviving collisions with the cosmic microwave background, through the Greisen–Zatsepin–Kuzmin limit.
Homework Statement
A pion traveling near the speed of light hits a nucleus and travels an average distance of 3.5fm before interacting. Estimate the time req. for the strong force to interact.
Homework Equations
The Attempt at a Solution
So are they saying that the pion hits the...
So I know the neutral pion decays as
\pi \rightarrow \gamma\gamma
my question is though, what forbids this from being an electromagnetic decay? I know it is not decaying via the strong force as there are no quarks resulting from decay. However, I do not see what forbids this from decaying...
Homework Statement
The neutral pion is an unstable particle that decays very quickly after its creation into two photons (“particles” of light: v = c, mo = 0). The pion has a rest-mass energy of 135 MeV. Consider a pion that has a kinetic energy of 90 MeV
1) Determine the v of this pion...
Hi,
I have a question about this decay: \pi^- \rightarrow e^- \overline{\nu_e}
there is a factor:
1 - \frac{v_e}{c}
what are these values, v_e,c, and why this quantity is equal to:
\frac{m^2_e}{m^2_\pi + m^2_e}?
Thank you
Ciccio
Quick question. If particles that mediate interactions are called gauge bosons, why isn't Pion considered a gauge boson. I'm pretty sure I've come across a few interactions mediated by it.
Hello! I'm afraid I've asked this before, a while ago, but I still don't completely understand. It's not a homework question as such, but I thought this might be an appropriate place to put it.
Homework Statement
Why is it that pions decay via pi^+ --> mu^+ + antimuon neutrino 98% of...
Homework Statement
The question is from "Advanced Physics" by Adams and Allday. It is from section 9 "The Physics of Particles", "Practice Exam Questions". It is question 10. The level of this study is between school and University.
I am uncertain about the answer to part c, ii (3rd...
Homework Statement
What is the speed of a pion if its average lifetime is measured to be 4.91E-8s? At rest, its average lifetime is 2.60E-6s. What is the particle's lifetime at rest?
Homework Equations
\Delta t = \Delta t0 / \sqrt{1-(v2/c2}
The Attempt at a Solution
I don't...
Hello! I was just wondering something...
Why is it that a negative pion always decays into a muon and antimuon neutrino? Why not an electron and antielectron neutrino? (and the same for a positive pion)
Any answers would be grately appreciated :-)
Samantha
How is it that \pi\^{\pm} have charges \pm e and \pi\^{0} has a charge of 0? The \pi\^{+} has one up quark and an anti-down quark, which doesn't add up to zero (same deal goes for \pi\^{-}, and the \pi\^{0} has a linear combination that doesn't seem to add up to zero.
Where have I gone wrong?
Problem:
A group of 'pi' mesons (pions) is observed traveling at speed 0.8c in a particle physics laboratory. (a) What is the factor 'gamma' for the pions? (b) If the pions' proper half-life is 1.8x10^-8 s, what is their half-life as observed in the lab frame? (c) If there were initially...
I have studied that the hadronic matrix element of pion decay
(Pi+->mu+ anti muon neutrino) is given as
<0|ubar gamma[mu](1-gamma[5])d|pion>.
The vector current does not seem to contribute, because it cannot connect a state of unnatural parity to hadronic vacuum. Only the axial and...
The positive W boson decays to a anti-muon and a muon neutrino, it should be a weak interaction.
And the positive Pion can decays to a anti-muon and a muon neutrino, too.
But the lifetimes of them are totally different, so why?
I know the positive Pion is composed of two quarks, but could you...
Hello, I understand that the non-zero (or non-small) rate for \pi^0 \rightarrow \gamma\gamma was historically a big motivation for the non-conservation of the axial current. I've been trying to work on problem IV.7.2 (p. 252) in Zee which asks to show that this amplitude vanishes if \partial_\mu...
Hello! I have to hand in this coursework tomorrow and I just wanted to check I had done it correctly so if someone could have a look I'd be really grateful... It's quite long...
Homework Statement
A negatively charged pion \pi^{-} has mass m=140MeV/c^{2} and lifetime 2.6 x 10^{-8}s.
a)...
Hello.
I've been having a hard time finding information about the following reaction:
e^{-}+n\rightarrowe^{-}+p^{+}+\pi^{-}
I hope you could give me some information about it.
I'm interested in energies for the incident e^{-} above 200MeV.
I think it has to do something with...
1. The statement, all variables and given/known data
I am studying the decay of the \eta-particle. Povh et Al, 'Particles and nuclei' say that a decay into 3 pions is not possible via the strong interaction. "For reasons of symmetry 3 pions (isospin equals 1) can not couple to zero isospin."...
Hi all,
I'm having trouble understanding the short lifetime on the neutral pion. I understand that in the residual strong interaction between nucleons, the range of the virtual pion is limited by Heisenberg's uncertainty relation for energy, which thus limits its lifetime. I don't...
How is it possible to have a pion that is made up of a linear combination of quarks? I mean, what are the physical constituents of the neutral pion? is it uubar or ddbar? Or does the linear combination mean that there is a 50 50 chance of a neutral pion being a made of uubar and ddbar?
I'm not sure whether this should go in this forum or the Advanced forum, but here goes.
Homework Statement
Given:
A pion+ decays into muon+ and neutrino,
\pi^+ \rightarrow \mu^+ + \nu
neutrino mass approaches zero, and
the pion is initially at rest.
Problem statement: Use...
I have one stupid question:
Is it true that the difference of proton and nucleon mass is due to the electromagnetic self-energy of the proton?
The same question about pi^0 and pi^- mass difference.
Consider this decay:
Pion+ -> muon+ + neutrino
It says that one can check the longitudinal polarization of the muon+ and this would confirm that the parity is not conserved. Can you explain what this means in simple terms?
The electromagnetic neutral pion decay is a three-point interaction: it decays into two virtual and charged Kaons or Protons, of which one then radiates a photon and then annihalates with the other to produce a second photon. (Obviously, a neutral particle cannot radiate photons directly)...
Hi first time user here.
I was hoping someone could please help me with the following question:
A moving neutral pion is observed to decay into 2 photons each with energy 80MeV, there being an angle 120deg between their trajectories.Calc
i)The total energy of the meson
ii)The momentum of...
Hi, i have a particle physics exam in 2 days and am confused on pion decay via the weak interaction, namely:
pi[-] ->muon + anti-muno neutrino
Thankyou
Ray Veldkamp